The aim of this project is to study mechanisms of immunity and immune evasion in schistosomiasis with the ultimate goal of developing an experimental vaccine employing defined antigens. A. Vaccination trials with purified paramyosin. Affinity purified or biochemically isolated paramyosin was shown to confer significant protection against challenge infection in 10 out of 12 experiments employing intradermal vaccination with BCG while vaccination with schistosome myosin or heterologous paramyosin was ineffective. However, schistosome extracts depleted of paramyosin were also protective suggesting the existence of other important immunogens in the intradermal model. B. Identification of E/S antigens recognized by vaccine antibodies. Metabolically labeled lung-stage schistosomula were shown to release four antigens of 30, 36, 64, and 100 Kd which are specifically recognized by mice multiply vaccinated with irradiated cercariae. A monoclonal antibody was produced against the 100 Kd component. These antigens are being investigated as new candidate vaccine immunogens. C. Dependence on antibody of praziquantel therapy. By assaying the binding of monoclonal antibodies to praziquantel treated worms recovered from athymic mice, an antigen of 200 Kd was identified which is specifically exposed as a result of drug treatment and therefore is a candidate target for the antibody response previously shown to be required in praziquantel therapy.